The present invention relates to a driving apparatus for automatically opening and closing a vehicular closing structure using power of a driving source such as a motor.
A tailgate provided to cover a rear end opening formed in a vehicle such as a station wagon which opens in a swing-up fashion tends to be relatively heavy and requires a large operating force to be opened. Due to this, it is a general practice to provide a so-called gas stay comprising a cylinder that is filled with oil and gas not only to assist in securing a required operating force in the opening direction but also to generate a holding force in an opened condition.
It seems to happen sometimes that the gas stay becomes short of thrust for holding the tailgate at the opened position due to a change in weight of the tailgate, a change in rotational resistance of a hinge portion and a change in ambient temperature.
As a technique for dealing with the inconvenience like this, a technique is proposed in JP-A-2001-107642 in which an opening and closing driving apparatus using a motor with reduction gears is provided between a tailgate and a vehicle body, then, when the movement of the tailgate in the closing direction from its own weight is detected, a clutch is engaged so as to allow a resisting force of the motor with reduction gears to be applied to the tailgate to thereby stop the closure of the tailgate from its own weight, and thereafter the tailgate is forcibly driven to be closed.
[Patent Literature No. 1]
JP-A-2001-107642
According to the structure of the related art, however, when the holding force of the tailgate's opened position is short, the tailgate is forcibly driven to be closed unconditionally, and nothing on cargo loading and unloading work is taken into consideration. In addition, while the movement of the tailgate in the closing direction due to the lack of required holding force of the tailgate's opened position is determined based on a descending amount of the tailgate, even in the event that the holding force of the opened position of the tailgate is in balance with the weight of the tailgate, since the traveling amount of the tailgate varies temporarily due to the effects of vehicle posture or the wind, it is not right in reality to determine the appropriateness of the holding force of the opened position of the tailgate based only on the descending amount of the tailgate.